Eukaryotes metallothioneins

Metallothioneins metal-binding proteins found in prokaryotes and eukaryotes that have been shown to be able to sequester and detoxify metals. 

All eukaryotes and some prokaryotes such as cyanobacteria synthesize metal binding proteins— known collectively as metallothioneins—in response to high concentrations of several metals including Cd. These are cysteine-rich, low molecular mass polypetides whose thiol functional groups have high affinity for soft cations such as Cd " " [36], All plants, including phytoplankton, synthesize class... 

Many different mechanisms to mediate heavy metal resistance in prokaryotes exist, and have been carefully reviewed elsewhere (Ralston and O Halloran 1990 O Halloran 1993). In eukaryotes, this job is done by metallothioneins which sequester heavy metal ions and make them unavailable to exert toxic effects (reviewed by Hamer 1986 Andrews 1990). In this regard, heme-hepoxin induces both heme oxygenase and MT expression in human promyelocytic leukaemia cells and mouse hepatoma cells (Alam et al. 1989). The authors suggest that MT may sequester the nontoxic metal zinc, which would otherwise compete with Fe for occupation of sites on Fe-dependent regulatory proteins such as the IRE-BP. Thus, it is possible that sequestration of metals by MT could mediate, not only the direct toxic effect of such metals (reviewed in Chap. 1, this volume), but... 

Carter, A. D., Walling, M. J., and Hamer, D. H., 1983, Distinct promoter and control sequences of an inducible metallothionein gene, in Enhancer and Eukaryotic Gene Expression (Y. Gluzman and T. Shenk, eds.), pp. 170-174, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York. 

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